1. Field of the Invention
The present invention relates to a CRT display unit and a power supply control method therefor, and more particularly, it relates to power supply control for extending the life of a CRT.
2. Description of the Background Art
A CRT display unit is connected to a central unit, such as a host computer, which generates a synchronizing signal and a video signal, to display an image of the video signal. In this case, it is recommended that power is applied to the CRT display unit independently of a power supply for the computer. If the power supply for the computer is also employed for applying power to the CRT display unit, this may lead to an excessive capacity of a power supply switch for the computer. Further, the CRT display unit is often installed in a position separated from the computer.
Under such circumstances, there have been proposed some CRT display units, whose power supplies are controlled to the power supplies on and off on the basis of signals from computers.
Japanese Patent Application Laying-Open No. 64-33586 (1989) describes a technique of detecting presence/absence of a video signal from a computer for on-off controlling a power supply for a CRT display unit on the basis of the result of the detection. In such a power supply control method, however, no video signal is present when a CRT intentionally displays a homogeneous black picture image, and hence the power supply for the CRT display unit is disadvantageously and erroneously turned off in this case.
On the other hand, each of Japanese Patent Application Laying-Open Nos. 60-1982 (1985) and 1-257893 (1989) describes a technique of detecting presence/absence of a synchronizing signal from a computer for on-off controlling a power supply for a CRT display unit on the basis of the result of the detection. In this power supply control method, however, the computer regularly transmits a synchronizing signal and hence, the power supply for the CRT display unit cannot be turned off unless a power supply for the computer is turned off or the CRT display unit is disconnected from the computer.
Further, there has been developed a technique of switching the screen of a CRT to display a homogeneous black image when the same display image continuously appears on the CRT for a constant period, in order to prevent burning of a fluorescent material which is applied to the screen of the CRT. Such switching of the display to a black picture image is often carried out by application software called a xe2x80x9cscreen saverxe2x80x9d, for example. When the xe2x80x9cscreen saverxe2x80x9d operates in such a manner, however, it is difficult to distinguish the screen of the CRT from that in a cutoff state of the CRT display unit. On the other hand, the power supply for the CRT display unit is not turned off upon such operation of the xe2x80x9cscreen saverxe2x80x9d. Consequently, the CRT display unit may be left intact in an ON state of the power supply therefor. This leads to wasteful power consumption, as well as to reduction in life of the CRT because of a continuous ON state of a heater provided therein.
Accordingly, a first object of the present invention is to eliminate the aforementioned disadvantage in a CRT display unit provided with a xe2x80x9cscreen saverxe2x80x9d.
According to the present invention, as hereinafter described in detail, a power supply control method is provided for a CRT display unit which is adapted to turn off a power circuit after a lapse of a predetermined period of time, as well as, to turn off a heater after a further lapse of a predetermined period of time when a xe2x80x9cscreen saverxe2x80x9d operates so that a CRT displays a homogeneous black picture image, in order to eliminate the aforementioned disadvantage.
However, the aforementioned xe2x80x9cscreen saverxe2x80x9d, which has been developed in order to prevent a CRT screen from burning, may be adapted to display various patterns of animations for the purpose of amusement, in addition to display of a homogeneous black picture image. A typical system of such a xe2x80x9cscreen saverxe2x80x9d is provided with tens of types of patterns, for example, while the user can produce such patterns himself in response to his liking.
In such circumstances, an applicable range of such a power supply control method is inevitably narrowed if the factor for starting the control for turning off the power supply for the CRT display is restricted to only the display of a homogeneous black picture image. Further, the software of the xe2x80x9cscreen saverxe2x80x9d, which has dependence on an operating system, requires dedicated programs for various systems such as DOS, Windows, OS/2, UNIX and the like, for example.
When the same image is displayed on the CRT for a constant period of time and it is necessary to drive the xe2x80x9cscreen saverxe2x80x9d, all input operations for the computer which are made by an operator are interrupted. There have been proposed some devices for detecting such an interrupted state of the input operations in a hardware manner and displaying a homogeneous black picture image, for example, in order to prevent the CRT screen from burning. According to Japanese Utility Model Publication No. 2-6467 (1990), for example, a CRT display unit includes a timer so that a video signal is converted to a blank signal if no input operation is carried out for a period of time which is previously set in the timer.
In order to implement the xe2x80x9cscreen saverxe2x80x9d in the aforementioned hardware manner, however, it is necessary to extensively modify the interior of the computer. Thus, a relatively high cost is required for such a modification. Further, such a modification is difficult to make for people other than a computer manufacturer.
Accordingly, a second object of the present invention is to implement a xe2x80x9cscreen saverxe2x80x9d in a hardware manner, with no need for an extensive modification of a computer body.
The present invention is first directed to a CRT display unit which is adapted to be connected to a central unit which generates a synchronizing signal and a video signal, for displaying an image of the video signal on the CRT display unit. This CRT display unit includes a power supply circuit which includes a main power supply and an auxiliary power supply, a power circuit, which is driven by the main power supply, including a high voltage circuit, a deflection circuit and a video circuit, a synchronous processing circuit for processing a synchronizing signal received from the central unit and supplying the processed synchronizing signal to the high voltage circuit and the deflection circuit, a video input processing circuit, which includes a video signal detector for detecting at least one of the presence or absence of a video signal output from the central unit, for processing the video signal and supplying the processed video signal to the video circuit, and a CRT having an anode which is supplied with a high dc voltage from the high voltage circuit, a deflecting yoke which is supplied with a deflecting current from the deflection circuit, a cathode which is supplied with a cathode drive signal from the video circuit, and a heater which is supplied with a current from the auxiliary power supply. According to each of first and second aspects as described below, the CRT display unit according to the present invention preferably includes the aforementioned elements in common.
According to the first aspect of the present invention, the CRT display unit further includes a main power supply controller for controlling the main power supply to turn on or turn off the power circuit when the video signal detector detects either the presence or absence of the video signal, a first timer for timing at least a period of time when the power circuit is turned off, and auxiliary power supply controllor for controlling the auxiliary power supply to turn off the heater after a lapse of a period of time previously set in the first timer.
According to the aforementioned first aspect of the present invention, the power circuit is first turned off when the xe2x80x9cscreen saverxe2x80x9d operates such that the CRT displays a homogeneous black picture image, i.e., when no video signal is present. When the period of time which is previously set in the first timer elapses upon continuation of such a state, the heater is then turned off. According to the present invention, therefore, it is possible to reduce wasteful power consumption, as well as to increase the life of the CRT. When a video signal is detected before the heater is turned off after turnoff of the power circuit, it is possible to quickly restore the CRT to an ordinary image display state.
In the aforementioned first aspect of the present invention, the main power supply controller preferably includes a second timer for timing the state in which no video signal is present, and a power circuit turnoff member for turning off the power circuit after a lapse of a period of time which is previously set in the second timer. In this case, the power circuit is not immediately turned off even if the xe2x80x9cscreen saverxe2x80x9d operates so that no video signal is present, whereby it is possible to prevent the power circuit from an erroneous turn-off operation when application software intentionally displays a homogeneous black picture image, for example. Consequently, it is possible to carry out delicate power supply control.
The period of time which is previously set in the first timer is preferably rendered variable, so that it is possible to carry out power supply control in response to a requirement by an operator.
Further, the main power supply controller preferably includes a blanking signal generator which supplies a picture blanking signal to the video circuit for a prescribed period of time when the video signal detector detects the presence of the video signal. As hereinabove described, the CRT is restored to an ordinary image display state when a video signal is detected before the heater is turned off after turn-off of the power circuit, while the image is rendered abnormal at the moment of such restoration. When a picture blanking signal is supplied for a prescribed period of time of 2 seconds, for example, at the moment of restoration as hereinabove described, it is possible to avoid displaying an abnormal or irregular image.
The CRT display unit according to the second aspect of the present invention comprises a timer which starts counting when the video signal detector detects absence of the video signal for timing a state in which no video signal is present, and the power supply circuit controller for controlling the power supply circuit to turn off the power circuit and the heater after a lapse of a period of time which is previously set in the timer, in addition to the aforementioned common elements.
According to the second aspect of the present invention, it is possible to reduce wasteful power consumption while preventing the power circuit and the heater from causing erroneous turn-off operations even if the application software intentionally displays a black picture image for a relatively short period of time, as well as, to increase the life of the CRT.
In each of the first and second aspects of the present invention, the CRT display unit preferably further includes a controller for controlling the power supply circuit to turn off the power circuit and the heater after a lapse of a prescribed period of time from detection of the absence of a synchronizing signal from the central unit. In this case, it is possible to turn off the power circuit and the heater also when a power supply for the central unit such as a host computer is turned off.
According to each of the aforementioned first and second aspects of the present invention, further, the video signal detector may not detect all color signals of red, green and blue but may detect only a red or blue color signal. Such a red or blue color signal is selected as the object of detection since a green color signal may be transmitted from the central unit to the CRT display unit as a composite video signal on which a synchronizing signal is superposed, and the circuit is complicated in this case since it is necessary to eliminate the synchronizing signal from the composite video signal if the green color signal is processed as the object of detection. When only a red or blue color signal is processed as the object of detection, on the other hand, the video signal detector can be simplified in structure. Nevertheless, the video signal detector may sufficiently detect only a color signal of red or blue in order to detect the absence of a video signal. Alternatively, the video signal detector may detect both of the red and blue color signals.
The present invention is also directed to a power supply control method for the aforementioned CRT display unit.
This power supply control method includes a step of controlling the main power supply to turn off the power circuit in response to absence of the video signal, and a step of controlling the auxiliary power supply to turn off the heater after a lapse of a predetermined period of time in such an OFF state of the power circuit.
In the power supply control method according to the present invention, the main power supply and the auxiliary power supply may be so controlled as to turn off the power circuit and the heater after a lapse of a prescribed period of time which begins with a state in which absence of the video signal is detected.
According to the present invention, further, attention is drawn to a computer of an open architecture type which is manufactured by IBM Corporation, for example, in order to attain the aforementioned second object. Such a computer of an open architecture type, whose interfaces are laid open to the public, includes some option slots so that the user can insert option boards for varying the computer functions as needed. The option boards can be manufactured by a manufacturer of such boards. According to the present invention, a graphics board can be used as one of such option boards. While a graphics board originally includes a circuit for supplying a video signal to a CRT display unit in order to display a picture which is based on an input signal from an external input device such as a keyboard, for example, hardware for implementing the xe2x80x9cscreen saverxe2x80x9d is added to such a graphics board according to the present invention.
In more concrete terms, the graphics board according to the present invention includes an input detection part for detecting at least one of the presence and the absence of an interruption request which is generated upon receipt of an input signal from the external input means for detecting presence of the input signal from the external input device, a timer starting a timing operation when the input detection part detects the presence of the input signal, and a signal supply member for supplying a blank signal to the CRT display unit as a video signal when the input detection part detects the absence of an input signal again before a lapse of a period of time previously set in the timer.
The external input decive typically includes an input operation device such as a keyboard and a mouse which are driven by the operator, as well as those based on an external communication system such as a network, a facsimile, a digitizer and a track ball.
When the external input device is formed by a keyboard, the input detector detects an address signal which is supplied as an output to an address bus in response to manipulation of the keyboard. When the external input device is formed by a mouse, on the other hand, the input detection part detects an interruption signal which is supplied as an output in response to manipulation of the mouse.
When such an external input device is formed by a plurality of elements such as a keyboard, a mouse and another external unit, the timer preferably starts its timing operation when the input detection part detects the presence of an input signal from any one of the external input devices. Further, the input detection part is preferably adapted to select the external input device that is generating an input signal whose presence is to be detected.
Thus, the present invention is further provided with a function of the xe2x80x9cscreen saverxe2x80x9d, which supplies a blank signal to the CRT display unit as a video signal when no input signal is received from the external input device for a prescribed period of time, with respect to an extension graphics board which is inserted in an option slot provided in a computer of an open architecture type.
Thus, according to the inventive graphics board, it is possible to provide a computer of an open architecture type with a xe2x80x9cscreen saverxe2x80x9d function simply by inserting the graphics board in its option slot. The input detection part which is provided in the graphics board simply monitors the presence of and/or absence of an interruption request generated upon receipt of an input signal from the external input device, whereby no modification is required on the body of the computer. In other words, the xe2x80x9cscreen saverxe2x80x9d function can be provided by merely modifying the graphics board, whereby it is possible to have the manufacturer of such a graphics board provide the xe2x80x9cscreen saverxe2x80x9d function.
According to the present invention, the graphics board is selected as an option board for providing a xe2x80x9cscreen saverxe2x80x9d function. The graphics board, which supplies a video signal to the CRT display unit and is connected to a line of an interface signal between a CPU and an input/output unit provided in the computer, is most suitable for detecting the absence of an input signal received from the external input device for a prescribed period of time and driving the xe2x80x9cscreen saverxe2x80x9d.
When the graphics board according to the present invention is employed, it is possible to drive a xe2x80x9cscreen saverxe2x80x9d with no regard to an operating system or application software employed in the computer to display a homogeneous black picture image on the CRT, thereby enabling regular application of the aforementioned power supply control method for a CRT display unit according to the present invention. Thus, it is possible to widen the applicable range of this power supply control method.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.